Vol. 51—1997 - NorthEastern Weed Science Society

152
opportu ity to use sethoxydim annually in corn-soybean, corn-peanut, or corncotton
otations. The wisdom of that would be questionable. However,
rotatio of sethoxydim with nicosulfuron or primisulfuron for control of
johnson rass could be beneficial in a system of continuous corn. Clearly,
there w'll be a continued need for education as HTC's come into the
marketp ace.
HTC' may have a major impact in some cases by allowing one to expand
product'on areas. An example is cotton production in the Blacklands of North
Carolin. This area, characterized by organic soils, has traditionally been a
major gain production region. Growers there are beginning to see cotton as a
potenti lly more profitable enterprise than grain crops. Cotton grows well in
these s ils, but weed control has been a major limitation because typical
soil-ap lied herbicides are ineffective on soils with high organic matter.
With th exception of pyrithiobac sodium, which will be available for the
first t e in 1996, postemergence herbicides for broadleaf weed control in
cotton ust be applied as directed sprays. Without assistance from soilapplied
herbicides, the height differential necessary to direct herbicides
often c nnot be obtained. The few people who have grown cotton in the
Blackla ds have had to resort to hand labor to clean up the crop, which of
course reatly reduces the profit potential. With bromoxynil and
posteme gence grass herbicides applied to bromoxynil-tolerant cotton, growers
have be n able to adequately control weeds without hand labor. When
glyphos te-tolerant cotton is commercialized, growers will have additional
tools f r weed management in this new production area.
Vari
but use
the gro
toleran
transge
for the
accord!
with an
rotatio
us benefits of HTC's may make weed management easier in some regards,
of HTC's will not necessarily reduce the management skills needed by
er. The grower will have to address the potential for drift to noncrops.
He will have to be vigilant in identifying fields planted to
ic crops so the proper herbicide is applied. He will have to be alert
population shifts that likely will occur and deal with them
gly. And in some cases, he will have to plan his management program
eye on controlling volunteers of herbicide-tolerant crops in
al crops.
HTC' of corn and soybean likely will not lead to major changes in
product on systems for these crops. Potentially, having the option to use
somethi g such as glyphosate postemergence may increase some growers'
confide ce in no-till. However, growers have already adopted no-till systems,
and for the most part, weed control has not been a major limitation.
Availab lity of HTC's such as glyphosate-tolerant soybean or glufosinatetoleran
corn could encourage more growers to follow a total post emergence
system. However, economics and time commitments necessary for other
enterpr ses on the farm will drive that decision more than simply availability
of HTC' • One could argue that post emergence systems are more IPM oriented,
and wit more and better postemergence options, growers might be more inclined
to move in that direction and use economic thresholds in their management
decisio s. This is unlikely. In both corn and soybeans, there already are
options for postemergence control of most weeds but very few growers have used
economi thresholds in their management decisions. Most fields are
suffici ntly infested that the question is not whether an application is
needed ut rather what to treat with. In the small percentage of fields where
populat ons are marginal enough to make one question the need for treatment,
the var ability in those low weed populations is so great that the intensity
of scou ing necessary to accurately use thresholds seldom can be economically
justifi d.
In c ntrast to corn and soybean, HTC's could encourage changes in cotton
product'on systems. In addition to expanding the area of production, as
discuss d above, HTC's likely will lead to more no-till cotton. Although
cotton creage planted no-till is increasing, fear of weed control failures
continu s to scare some growers away from no-till cotton.